The premise is spectacular. Mieville did an amazing job world building two cities in the same geographic footprint that have separate languages, customs, mannerisms and aesthetics. They remain separate because the citizens don't acknowledge each other under the threat of customs and the law.

It's a noir detective story through and through. The prose is overwrought and full of garden path sentences. It reinforces the cramped warren-like feel of Beszel but I don't think it was intentional. I kept having to reread sentences because their baroque construction. It really took me out of the story. It's still worth a read.